Efficiency Improvement of a Dual-input LLC Converter for PV Applications using Burst-mode Control Strategy

Although LLC resonant converter is well-known for its high efficiency, its light load efficiency still cannot meet the ever-growing market requirements. This paper applies a burstmode (pulse-skipping) control strategy to improve the light load efficiency of a dual-input LLC resonant converter which interfaces with two PV panels. This topology is a dual half-bridge LLC circuit with four active switches. A phase-shift pulse width modulation (PWM) control is employed to implement independent maximum power point tracking (MPPT) for each PV panel and suitable burst-on time for each load condition is selected to maximize the efficiency of burst-mode operation. The switching frequency and phase shift are varied to control the converter voltage gain. Zero-voltage-switching (ZVS) is realized in all switches over the entire range of source voltage and load conditions. A 200-W prototype was setup to verify the proposed control strategy. The input voltage range was selected to be 25 V to 45 V with an output voltage regulated at 200 V DC. Experimental results show that the proposed burst-mode control strategy can significantly improve the converter light load efficiency by around 6% maximum and waveforms match the simulation results fairly well.